Printing processes utilize a vast array of different technologies to transfer written content to various distribution media. Organizations using varying printing processes include modest-volume quick printers, book and financial publishers, newspaper companies, forms companies, all sizes of commercial printers (for advertising etc.), and, publication printers (for magazines and periodicals). These types of organizations have a common process whereby information is transferred from some original layout form to an intermediate aluminum or polyester plate material which is then hung on a standard printing press to enable multiple identical replication of that information on paper or some similar print media.
This process has typically been performed by optically creating a polyester film which contains the information, optically transferring the information from the film to a plate material by use of a light transfer or contact to a light-sensitive chemical emulsion which is bonded to the plate, and then hanging the developed plate on a press in alignment (one for each color separation desired). The plates rotate along with the press cylinder and alternately come in contact with ink rollers and then an intermediate transfer blanket. The ink which is accepted by the transfer blanket then transfers the information to the paper during rotational contact.
Recently the development of computer-to-plate, hereinafter C2P, systems and processes have provided alternative printing options. The C2P process eliminates the film as an intermediate transfer mechanism and allows the optical exposure of the plate directly. This reduces the number of steps required in the printing process of the information and potentially reduces the cost related to the generation of the intermediate film and its handling. C2P systems more readily allow a process which creates plates for shorter-run printing (below around 50,000 impressions).
In basic terms, a C2P system accepts input jobs/pages written in a page description language, for example, POSTSCRIPT.RTM.. These jobs are controlled through execution by priority and scheduling workflow software. Jobs are then sent through a raster image processor to a platemaker for exposure. The data is being transformed throughout this process. The platemaker engine takes this data and prints it on a metal sheet of aluminum which is later notched, bent, hung on the press, inked and made ready to image paper. An imaging engine and process for imaging a plate is described in commonly owned U.S. Pat. No. 5,345,870, hereby incorporated by reference into the present application.
The inclusion of a C2P system into a printing operation suggests a greater extent of automation which can be achieved. A full C2P process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate. As such, C2P is not only an improvement in the specialized equipment but also in the process which utilizes that equipment. Viewing C2P as a process includes a high level of workflow management to replace manual effort with computer-driven effort with a goal to increase productivity and efficiency. Workflow encompasses such concepts as queue management, color calibration, revision control, press consumables control, inventory tracking, job and cost tracking, etc.
Also included in the automation of a C2P system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker engine and it is desirable to reduce the amount of operator handling involved. Unexposed plates are normally supplied in packages of 25 to 100 with interleaf sheets between the plates for protecting the sensitive emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates needs to be loaded into a supply area of a platemaker in a manner to keep the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheet from the stack. These functions are optimally performed within a covered light-tight environment to prevent unintentional exposure of the light sensitive plate surface. The platemaker engine requires plates of varying sizes and formats on demand. It is beneficial to present a variety of plate sizes and formats to an automated mechanism for selecting the plate needed by the platemaker engine. It is important to be able to reload the plate supply area without interrupting the operation of the platemaker engine. These functions generally will maximize the output of the platemaker engine, by eliminating time which an operator would manually handle the plates and during which the platemaker engine might be interrupted.
Accordingly it is an object of the present invention to provide an automated C2P system having a workflow software capable of controlling and sequencing the tasks performed by the C2P system from accepting a job input to the system as POSTSCRIPT.RTM. and output the job from the system as exposed images on printing plates.
It is a further object of the invention to increase productivity and efficiency in a C2P system by providing automated queue management.
It is a specific object of the invention to automate the operation of supplying plates on demand from a plate storage area within a C2P system to the platemaker engine.
It is a further object of the invention to provide a plate handling mechanism to position a plurality of plate cassettes containing varying plate sizes within the plate storage area, making a desired plate cassette accessible to a plate picking mechanism.
It is another object of the present invention to automatically remove and discard the interleaf sheets from between plates after a plate is individually removed from the stack of plates.
It is another object of the invention to automatically pick a plate from the top of a stack of plates and deliver the plate to the platemaker engine in a manner which accommodates a variety of plate sizes and formats.